1. Field of the Invention
The present invention relates to a mode processing circuit for a multiple operation mode electronic apparatus such as a video tape recorder, a tape deck, a video disc player, a compact disc player and so on.
2. Description of the Prior Art
Various operation modes, such as a playback mode, a rewind mode and the like are available in a known video tape recorder (hereinafter simply referred to as a VTR). To change these operation modes, it is necessary to switch the VTR or to move its brake and pinch roller into and out of engagement.
If a plunger is used to switch the mechanism, the change of the operation mode can be made substantially in a moment. The employment of the plunger, however, causes a large current to flow upon its actuation. Also, in the normal operation mode, a current must flow continuously, requiring a large power supply circuit which consumes a large amount of power.
It is therefore proposed to employ a motor instead of the plunger. When a motor is used together with a gear mechanism, atthough it is small in size, the necessary driving power to switch the mechanism is generated. Further, the employment of the motor can reduce the power consumption and allow the power supply circuit to be small in size. However, when a motor is used to switch the mechanism, the transition (switching) of its mode takes a lot of time. For example, it takes about 2 seconds for the VTR to change from the stop mode (STOP) to the playback mode (PB); it takes about 1.5 seconds for the VTR to change from the playback mode (PB) to the stop mode (STOP); and it takes about 1.8 seconds for the VTR to change from the stop mode (STOP) to the recording mode (REC).
Accordingly, when a user intends to press a second operation key after a first operation key has been depressed, the user must not press the second operation key until the VTR finishes changing to the mode commanded by the first key.
This is very inconvenient for the user, so it is proposed to stack input commands issued by pressing the operation keys.
Let it now be assumed that as, for example, illustrated in FIG. 1, the VTR is placed in the stop mode before time point t.sub.1 and that a recording key is pressed at time point t.sub.1. Then, the mode of the VTR (mechanism) begins to change from the stop mode to the recording mode at time point t.sub.1.
If a stop key, for example, is pressed at time point t.sub.2 during this transition period, this stop key is valid for the recording mode which is the mode after the mode is changed, so that the command instructing not the recording mode but the stop mode after the mode transition, is stacked in the mode stack.
When the mode transition of the VTR is ended at time point t.sub.3, the VTR is placed in the recording mode (REC). At that time, the stop mode command stacked in the mode stack at time point t.sub.2 is read out and the processing of this command is executed.
Accordingly, the VTR begins the transfer to the stop mode at time point t.sub.3 and is placed in the stop mode at time point t.sub.4. Even though a pause key is pressed at time point t.sub.5 in the stop mode, the pause mode (PAUSE) is useless for the stop mode. Hence, the command issued by pressing the pause key is not executed.
As described above, according to this mode stack system, it becomes posiible to remove the cumbersome requirement that the user must not press the next operation key until the mode transition of the VTR is ended (even if the next key is pressed, this will be neglected). However, the above mentioned mode stack system has the following defect.
If the stop key is pressed at time point t.sub.2 and the pause key is then pressed at time point t.sub.a as, for example, shown in FIG. 2, since this pause key is valid for the recording mode, which is the mode after the mode transition (if the pause key is depressed in the recording mode, the VTR is placed in the recording pause mode (REC PAUSE)), and the mode stacked in the mode stack is changed again from the stop mode to the recording pause mode.
Accordingly, the mode of the VTR is moved to the recording pause mode at time point t.sub.3 and the VTR is placed in the recording pause mode at time point t.sub.4.
Although the stop key and the pause key are pressed in the same sequential order as that of FIG. 1, the VTR is placed in an operation mode different from that in FIG. 1 in this case because of the timing of the depression of the pause key vis-a-vis the actual mode shifting of the VTR.
In other words, if a plurality of valid operation keys are depressed during the mode transition period, the mode stacked in the mode stack is renewed to the mode suggested by the operation key that was last pressed by the user and the modes commanded by the previously-pressed operation keys are all neglected. Accordingly, the operation mode of the VTR becomes different depending on the timing at which the user presses the operation keys (depending on whether the VTR mode was in the process of being changed or was already changed when the keys were pressed).
To overcome the above mentioned shortcomings, an improved mode stack system is proposed, in which the mode stack is arranged to have a plurality of stages to sequentially stack the input modes and to execute the modes sequentially.
This mode stack system having a plurality of stages, however, must remove useless or invalid modes stacked in the mode stack by optimizing the mode stacked. This makes a program of a mode control microcomputer complicated and takes a lot of time for such removal. This defect becomes serious particularly when 8-bit mode data is processed by a CPU (central processing unit) which is capable of providing only a 4-bit comparing command. Further, an area for the mode stack must be provided in a RAM.